1. Field of the Invention
This invention relates to a solder alloy suitable for bonding a terminal etc., for example, in an inside of an electronic component, and, more particularly, relates to a solder alloy having excellent thermal shock resistance.
2. Related Art of the Invention
Conventionally, a structure which contains a piezoelectric resonator in a package which does not obstruct oscillation of a piezoelectric resonator has been widely used in piezoelectric resonance components, etc. In these types of piezoelectric resonance components, the piezoelectric resonator and an electrode and a terminal, etc. which are disposed on the package are bonded with solder.
In the solder for bonding to the inside of an electronic component, i.e., a so-called internal solder, heat stress resistance at the time of the soldering for mounting an electronic component in a printed circuit board etc. is required. Therefore, it is strongly required that the internal solder be difficult to melt by heat stress at the time of mounting electronic-component and be characterized by being difficult to cause cracks, etc.
Conventionally, an eutectic solder of Sn--Pb with a comparatively high melting point and Sn--Sb eutectic solder are used as the internal solder to withstand the heat stress in mounting the electronic components.
When prevention of diffusion of solder to the electrode surface is required, a Pb-rich composition eutectic solder such as an eutectic solder of the composition which includes 60 wt % of Sn and 40 wt % of Pb is used.
When a prevention of solder diffusion such as by forming Ni barrier phase on an electrode surface is desired, a Sn-rich solder such as Sn--Sb system eutectic solder is used.
However, the above described internal solders have a problem in that the thermal shock resistance is not sufficient.
In Sn--Pb system eutectic solder, a Pb-rich phase (alpha-phase) and a Sn-rich phase (beta-phase) grow. However, there is the problem that a correlation crack is produced between the alpha-phase and the beta-phase or that a crack in the alpha-phase is produced.
In Sn--Sb system solder which does not contain Pb, such as the above Sn--Sb system solder, the above described cracks are hardly caused. However, the Sn--Sb system solder has a high Young's modulus. Therefore, when a heat stress is imposed, the solder easily mechanically damages the electrodes, and easily causes electrode peeling, etc.